The present disclosure relates to an illuminating apparatus used to illuminate hard-copy documents for digital recording, such as in digital scanners, facsimile machines, and digital copiers.
In office equipment, such as digital copiers and facsimile machines, original hard-copy documents are recorded as digital data using what can be generally called a “scanner.” In a typical scanner, a document sheet is illuminated and the light reflected from the document sheet is recorded by a photosensitive device such as a CCD (charge coupled device) or CMOS (complementary metal oxide semiconductor) array, to be converted to digital image data. In one embodiment, a narrow strip of the document sheet is illuminated as the sheet is moved through a document handler, or the photosensitive device is moved relative to a platen on which the document sheet is placed.
One type of illuminator useful in document scanning includes a light-transmissive element that exploits internal reflections to direct light from one or more point sources, such as light emitting diodes (LEDs) to emerge in substantially parallel rays from an exit surface of the element toward a document.
Designing an illuminator for a scanner presents challenges in providing, among other aspects, an even illumination along the narrow strip of the document, as well as providing a suitable illumination profile across the narrow strip.
The angular distribution of light produced by the illuminator at the document can vary in the fast scan direction, depending upon the illuminator architecture. Irregularities in the illumination level in the illuminated area can result in defects in the image data, particularly in the case of discrete light sources, such as LEDS. While light guides are able to focus light with high efficiency on the imaging area of the platen, it has been found that glossy document surfaces which are uneven, e.g., crumpled or curved from the platen, may reflect the light toward the photosensitive device unevenly, resulting in bright spots in the image.